Effect of Upright Posture on Endothelial Function in Women and Men

Women, orthostatic tolerance, and POTS: a narrative review

Young women experience orthostatic intolerance to a greater degree than men. Numerous physiological pathways could be responsible for this intolerance in both healthy and pathophysiological conditions. This review discusses sex differences in hemodynamics, ventilation, autonomic control, and cerebral blood flow. Further, we discuss these phenomena and their potential exacerbations in postural orthostatic tachycardiac syndrome (POTS). After normalization for body size women have lower stroke volume and blood volume, and while upright women have reduced ventilation, reduced venous return likely from attenuated respiratory pump and skeletal muscle pump activity, augmented parasympathetic withdrawal, attenuated neurovascular transduction of sympathetic outflow, and increased vasodilatory capacity compared to age-matched men. Women have greater middle cerebral artery blood velocity, potentially impaired cerebral dynamic autoregulation (depending on the timing), yet similar cerebrovascular reactivity to carbon dioxide exists between the sexes. Thus, we suggest that the greater incidence of orthostatic intolerance in women is primarily due to hemodynamic control and autonomic function; however, the enhanced parasympathetic withdrawal while upright could theoretically influence cerebral vasodilatory capacity and is proposed as a possibility in need of further investigation. POTS physiology is described briefly due to its increasing prevalence via post-COVID infections. We summarize some potential physiological changes in POTS including hemodynamic and ventilatory control, and we highlight that cerebral blood flow control is impaired and likely plays a role in the symptomology of POTS.

Pilot Assessment of Piezoelectric Transducers as a Cost-Effective Alternative to EndoPAT

INTRODUCTION

Current microvascular assessments may not be practical or accessible requiring experienced personnel and/or ongoing equipment costs. Piezoelectric transducers can reliably obtain finger blood pressure waves, similar to peripheral arterial tonometry devices; thus, they could be used to estimate microvascular function. We aimed to validate piezoelectric transducers as an alternative measure of microvascular function compared to EndoPAT.

METHODS

Twenty-five adults (aged 20-64 years) completed reactive hyperemia (5 min forearm circulatory occlusion and 3 min recovery) with piezoelectric transducers on the middle fingers and EndoPAT probes on the index fingers. Average area under the curve (AUC) of the pulse wave signal for the occluded and control arms was determined at baseline, every 30 s post-occlusion, and 10 s around the peak response. Microvascular function index (MFI) was calculated as the ratio of AUC post-occlusion to AUC baseline in the test arm, then normalized to the same ratio in the control arm. MFI at each time point was correlated with the reactive hyperemia index (RHI) from the EndoPAT.

RESULTS

The greatest significance was found between RHI and MFI at 10 s around the peak response (Spearman's r = 0.67, p = 0.0002; Pearson's r = 0.76, p = 0.00001).

CONCLUSION

MFI is a reusable and user-friendly microvascular function assessment that could provide better access to vascular health screening.